The present invention relates to an internal combustion engine control device which is applied in a multi-cylinder internal combustion engine.
An internal combustion engine disclosed in Japanese Laid-Open Patent Publication No. 2014-31723 has, in correspondence with each cylinder, a first fuel injection valve that directly injects fuel into the cylinder, and a second fuel injection valve that injects fuel into an intake passage. The internal combustion engine control device disclosed in this document conducts an imbalance determination in order to detect variations in air-fuel ratio among the cylinders.
First, a first imbalance determination is conducted when the engine is operated by injecting fuel from the first fuel injection valve only. A second imbalance determination is conducted when the engine is operated by injecting fuel from both the first and second fuel injection valves after the first imbalance determination. If any variations in air fuel ratio are detected among the cylinders by the second imbalance determination, a third imbalance determination is conducted when the engine is operated by injecting fuel from the second fuel injection valve only. Thus, abnormal states in the first and second fuel injection valves are detected with high accuracy.
An internal combustion engine having an exhaust recirculation device, which recirculates some of exhaust flowing in an exhaust passage into an intake passage, is known. In an internal combustion engine of this type, exhaust is likely to be recirculated into the intake passage during an imbalance determination.
In the internal combustion engine disclosed in Japanese Laid-Open Patent Publication No. 2014-31723, the injection opening of the second fuel injection valve is located inside the intake passage. Therefore, when some of exhaust flows in the intake passage, deposits derived from components contained in the exhaust are likely to stick to and accumulate on the injection opening of the second fuel injection valve, from which fuel is not injected during the first imbalance determination. An accumulation of deposits on the injection opening of the second fuel injection valve narrows the area of the injection opening, which may result in a decrease in quantity of fuel injected from the second fuel injection valve. Therefore, when fuel is injected from the second fuel injection valve, the actual quantity of fuel injected from the second fuel injection valve is likely to be smaller than a target quantity of fuel injected therefrom.